ABSTRACT
Maintenance associated with an aging bridge stock has become a major problem for bridge owners and managers throughout Europe. In response to this problem, there has been increased interest in the use of probabilistic methods for the assessment of aging bridges. The purpose of using probabilistic methods to assess the performance of a bridge is to avoid unnecessary repair/rehabilitation and/or to optimise those repairs that are shown to be necessary.
This paper presents a probabilistic basis for assessment of railway infrastructure. Full-scale assessments of two steel-truss railway bridges are used to illustrate the methodology and impetus for probabilistic assessment. Finite Element (FE) models were created and traditional deterministic assessments were carried out. Subsequently, stochastic modelling was performed on the variables relating to the loading and strength properties of the bridges in question. This stochastic modelling allowed for calculation of the failure probability associated with various limits states. The stochastic distributions employed for one bridge are illustrated in Table 1. The majority of the distributions were taken from guidance in a publication by the Danish Roads Directorate (2004). Models and parameters for stochastic variables.
Variable
Dist
μ
CoV
Yield Strength
Log N
297 MPa
0.11
Uncertainty – Yield Strength
Log N
1
0.10
Dead Load Stress
Norm
17.1 MPa
0.05
Uncertainty – Dead Load
Norm
1
0.05
SDL Stress
Norm
13 Pa
0.10
Uncertainty – SDL
Norm
1
0.05
Fraction of RU loading
Gumb
0.66
0.20
Uncertainty – Live Load
Norm
1
0.15
ε Increment
Norm
0.14
1.00
The results of one assessment were employed to strategize a Structural Health Monitoring (SHM) System and testing regime for the bridge in question; the Boyne Viaduct, located in Drogheda, Ireland. Figure 1 illustrates the FE model developed for the Boyne Viaduct. FE model of the Boyne Viaduct. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig45_1.tif"/>
A combination of triaxial accelerometers and rosette strain gauges were installed on the Boyne viaduct. The effect of the instrumentation and testing on the assessment was considered by way of uncertainty. It was shown that the variation in the uncertainty associated with yield strength would reduce from 10% to 3.5%, corresponding to an increase in the reliability index from 3.39 to 4.44. The potential benefits to bridge owners are evident from the results, which show that specific members can be shown to have sufficient capacity under service loading, even after having failed a deterministic assessment.
